The present invention concerns a radial rotary union joint and a bush for same, which forms a radial sliding ring seal. The bush comprises a hollow-cylindrical main body whose inner cylindrical surface forms a sliding sealing surface which is divided by a peripherally extending inner groove into a first and a second sliding seal surface. The bush further has a cylindrical outside surface which is divided by a peripherally extending outer groove into a first and a second outside surface, wherein the wall portion separating the inner and the outer grooves has at least one bore connecting the two grooves and wherein the first and the second outer outside surfaces can be sealed off by a respective stationary sealing ring in relation to a housing embracing the bush.
The corresponding rotary union joint has as an essential part at least one such above-defined bush and in addition also comprises a housing for accommodating the bush and possibly has at least one ball bearing between the housing and a rotating shaft embraced by the bush. In that case the bush can be adapted directly to the outside diameter of the corresponding shaft so that the sliding sealing surfaces of the bush slide directly against the shaft surface when the shaft rotates relative to the bush.
However an inner hollow cylinder or a sleeve on which the bush slides can possibly also be part of the rotary union joint, in which case that inner hollow cylinder or the inner sleeve is in use connected fixedly and in sealed relationship in the housing to a corresponding rotating shaft. In that case the sleeve can have the outer cylindrical sliding sealing surfaces which come into sealing and sliding engagement with the sliding sealing surfaces on the inside of the bush. Accordingly that sleeve can take over the function of the rotating shaft in relation to the bush so that all critical interfaces which necessitate very precise surface machining and a high surface quality are disposed within the rotary union joint while the interfaces in relation to the rotating shaft and to external connections are respectively stationary and thus less critical and in that respect for example can also be produced and supplied by different manufacturers.
The shaft can also be a short shaft portion forming a part of the rotary union joint, wherein that shaft portion ends for example in a short flange which can be sealingly connected to a rotating shaft of a corresponding machine.
Hereinafter consideration will be given to the simpler variant in which the bush slides directly on the corresponding outside surface of the shaft or a shaft portion. When a sleeve is interposed, all considerations similarly apply insofar as the sleeve is considered as a part fixedly connected to the shaft or a constituent part of the shaft.
The outer groove is acted upon by a pressurised fluid by way of an outer housing, the fluid passing through the bore which connects the outer and the inner groove into the inner groove and thus to the outside periphery of the shaft which in turn has one or more bores communicating with a correspondingly axially extending passage in the interior of the shaft.
In that way it is possible, during rotation of a shaft, to feed a fluid from the exterior into and through the shaft or conversely out of the shaft and through the bush outwardly, wherein the shaft rotates in the bush and the surfaces sliding against each other of the shaft and the bush form a sliding seal.
It will be appreciated that the friction occurring in such a sliding seal is desirably to be kept as low as possible, especially as at relatively high rotary speeds a corresponding frictional heat is also generated because of the friction involved, and with excessive friction that could also lead to the bush seizing on the shaft. On the other hand as little fluid as possible should escape between the surfaces sliding against each other, especially when dealing with a corresponding leak is relatively complicated and expensive and difficult.
The sliding sealing surfaces of the bushes are therefore produced with very close tolerances and a high degree of precision, and likewise also the complimentary sliding sealing surfaces on a shaft or possibly a corresponding sleeve which is to be fixed on the outside periphery of the shaft, in order to provide a sealing gap which is as narrow and uniform as possible but which nonetheless allows the cylindrical surfaces to slide easily against each other.
However, particularly when the fluid is under high pressure, certain deformations of the bush are inevitable, and they can also influence the configuration of the sealing gap between the surfaces of the shaft and the bush, which slide against each other.
The attempt has already been made in DE 38 06 931 to deliberately provide for such deformation by a suitable choice of the width and depth of the outer groove as well as the position of an outer stationary seal in the shaft in such a way that there was a tendency for the inner sliding sealing surface to be of a conical shape, in which case the larger diameter of the cone was to be directed towards the inner groove and the smaller diameter thereof was respectively facing away from the inner groove.
The result of that however was that the sealing gap enlarges somewhat in the region adjoining the transfer grooves and becomes somewhat narrower at the ends remote from the groove.
That approach however still appears to be worthwhile at comparatively low pressures up to about 100 bars.
In the meantime however it has been found that such a bush configuration, even if it can have a tendency to contribute to a reduction in the leakage rate, only functions satisfactorily at up to pressures of about 100 bars. When higher pressures are involved generally more complicated and expensive systems are used, in which corresponding bushes are for example of a multi-part configuration or are of great axial length to avoid excessive deformation of the bush which otherwise could no longer be tolerated because such deformation would have excessively high leakage rates or could result in seizing of the bush on the shaft and thus damage to the bush or the shaft.
In comparison with that state of the art the object of the present invention is to provide a bush having the features set forth in the opening part of this specification, which even at pressures of markedly above 100 bars and also at relatively high rotary speeds permits the transfer of fluid at low leakage rates. In particular the invention seeks to provide a corresponding bush which still functions well and can be used at pressures of more than 150 bars and in particular at pressures of more than 200 bars.
In that respect the bush should be axially relatively short in order not to take up excessive space.
For a bush having the features set forth in the opening part of this specification that object is attained in that the side surfaces of the inner groove are of the same size within a tolerance range of +20% and −35% as the side surfaces of the outer groove and an outer stationary seal is positioned on the outside surface of the side surface in the axial direction in such a way that it is at an axial spacing from the axially outer end of the sliding sealing surfaces, which corresponds to at least 40% and at most 55% of the respective axial length of the sliding sealing surface.